The properties of fluoropolymer membranes, for example, porous PTFE membranes, including their mechanical strength, chemical resistance or inertness, non-adhesiveness, excellent dielectric property, thermal stability at high temperature and low coefficient of friction make them very attractive for various applications. However, for certain applications, it will be beneficial to modify the surface of PTFE without affecting its intrinsic properties. Efforts have been made to modify the surface and the chemical properties of PTFE membrane in order to improve the suitability of the membrane for specific applications. For example, efforts have included surface coating, blending, high energy surface modification, for example, broad band ultraviolet radiation or BBUV, where the membrane is exposed to a UV radiation of wavelength 250-450 nm, and plasma treatment, free radical, and ozone etching, atomic layer deposition, and synthesis of modified PTFE-like polymers. However, most of the efforts were focused on high energy treatment such as with BBUV or plasma. Though the exact mechanism of these surface modification approaches is not reported, it likely results from the formation of free radicals by main-chain bond scission since C—C bond strength is known to be ˜40% lower than F—F bond. If a majority of the radical results from C—C scission or main polymer chain scission, it could decrease the mechanical and the chemical stability of the PTFE membrane. It is also known that plasma treatment is limited to the surface of the membrane which makes such modification less stable during a prolonged period of time.
The foregoing shows that there exists an unmet need for a surface modification of porous fluoropolymer membranes or supports to provide hydrophilic fluoropolymer porous membranes which are stable, and wherein the surface modification does not significantly affect the mechanical strength of the porous fluoropolymer supports or the resulting composite porous membranes.